What is your computer system and Firefox?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Mac Book Pro IOS 10.9.5 8GB Firefox 42. Problem began when Firefox update downloaded several days ago.

Same behavior in safe mode. Firefox hangs after being used once or twice.

I have noted that when Firefox is hanging, clicking the full screen arrows in upper right hand corner wakes up the system and allows input. Cant understand that at all.

Appreciate help.

I've called the big guys to help you. Good luck.

Install an older version of Firefox {web link}

Thanks for trying. No response yet.